Prompting language influences diagnostic reasoning and accuracy of large language models
Pith reviewed 2026-05-20 10:21 UTC · model grok-4.3
The pith
Large language models achieve higher diagnostic accuracy and better reasoning when prompted in English than in French.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The study compared English and French prompting on diagnostic reasoning and accuracy using 180 vignettes across 16 specialties scored on an 18-point scale by two physicians. Four of the five models performed better in English with mean differences of 0.37 to 0.91 (adjusted p < 0.05). The performance gap included multiple aspects of reasoning such as differential diagnosis, logical structure, and internal validity. Only the o3 model showed no overall language effect.
What carries the argument
Direct comparison of identical clinical vignettes presented in English versus French, evaluated with a structured 18-point physician scoring rubric that assesses both diagnosis accuracy and reasoning quality.
If this is right
- Prompting language remains a critical determinant of LLM clinical performance.
- The performance gap spans differential diagnosis, logical structure, and internal validity.
- Equitable linguistico-cultural deployment of LLMs worldwide requires attention to language effects.
- One model showed no overall language performance difference while the others did.
Where Pith is reading between the lines
- Model developers may need to balance training data across languages to narrow these performance gaps.
- Similar language effects could appear when using other non-English languages not tested here.
- Clinical applications in French-speaking regions might require language-specific prompting strategies or model selection.
Load-bearing premise
The 180 clinical vignettes and the 18-point physician scoring scale provide an unbiased, language-neutral measure of diagnostic performance that generalizes beyond the specific cases chosen.
What would settle it
A replication using a fresh set of clinical vignettes or a different physician scoring method that finds no consistent English advantage across the same models would undermine the central claim.
Figures
read the original abstract
Large language models (LLMs) are increasingly explored for clinical decision support, yet most evaluations are conducted in English, leaving their reliability in other languages uncertain. Here we evaluate the impact of prompting language on diagnostic reasoning and final diagnosis accuracy by comparing English and French performance across five LLMs (o3, DeepSeek-R1, GPT-4-Turbo, Llama-3.1-405B-Instruct, and BioMistral-7B). A total of 180 clinical vignettes covering 16 medical specialties were assessed by two physicians using an 18-point scale evaluating both diagnosis accuracy and reasoning quality. Four of the five models performed better in English (mean difference 0.37-0.91, adjusted p < 0.05), with the gap spanning multiple aspects of reasoning, including differential diagnosis, logical structure, and internal validity. o3 was the only model showing no overall language effect. These findings demonstrate that prompting language remains a critical determinant of LLM clinical performance, with implications for equitable linguistico-cultural deployment worldwide.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper claims that prompting five LLMs (o3, DeepSeek-R1, GPT-4-Turbo, Llama-3.1-405B-Instruct, BioMistral-7B) in English versus French on 180 clinical vignettes across 16 specialties yields higher diagnostic reasoning and accuracy scores in English for four models (mean differences 0.37-0.91, adjusted p < 0.05), as evaluated by two physicians on an 18-point scale covering diagnosis accuracy, differential diagnosis, logical structure, and internal validity; only o3 showed no overall language effect.
Significance. If the result holds after methodological clarification, the work is significant for highlighting language as a determinant of LLM clinical performance and for underscoring risks to equitable deployment in non-English medical settings. The multi-model design and physician-based scoring on real-world vignettes add practical value, though the absence of reported controls limits immediate generalizability.
major comments (3)
- [Methods] Methods (vignette construction and translation): The manuscript provides no details on vignette selection criteria, whether vignettes originated in English and were translated to French, or any equivalence validation (back-translation, professional medical review, or cultural adaptation). This is load-bearing for the central claim because unvalidated translations could systematically alter perceived logical structure or internal validity, confounding the reported mean differences of 0.37-0.91.
- [Methods] Methods (scoring and reliability): No information is given on inter-rater reliability for the 18-point physician scale or on whether raters were blinded to output language. Without these, it is unclear whether the observed advantages in differential diagnosis and reasoning quality reflect model capability or scoring artifacts tied to language-specific phrasing.
- [Results] Results (statistical reporting): The abstract states adjusted p < 0.05 but the paper does not specify the exact tests, multiple-comparison corrections, or adjustments for vignette difficulty or model factors. This weakens confidence that the language effect is robust rather than an artifact of analysis choices.
minor comments (2)
- [Methods] The prompting templates for each language and model should be reproduced verbatim in the supplement to allow exact replication.
- [Results] Figure or table presenting per-model, per-language scores would improve clarity over summary statistics alone.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed feedback, which identifies key areas where additional methodological transparency will strengthen the manuscript. We address each major comment below and will incorporate the necessary clarifications in the revised version.
read point-by-point responses
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Referee: [Methods] Methods (vignette construction and translation): The manuscript provides no details on vignette selection criteria, whether vignettes originated in English and were translated to French, or any equivalence validation (back-translation, professional medical review, or cultural adaptation). This is load-bearing for the central claim because unvalidated translations could systematically alter perceived logical structure or internal validity, confounding the reported mean differences of 0.37-0.91.
Authors: We agree that the Methods section requires greater detail on vignette construction and translation to support the central claims. In the revised manuscript, we will add a new subsection specifying that the 180 vignettes were drawn from publicly available English-language clinical case repositories used in medical education, that all vignettes originated in English, and that French versions were produced via professional medical translation followed by independent back-translation and review by a second bilingual physician to confirm clinical equivalence and preserve logical structure. These additions will directly address concerns about potential translation-induced confounds. revision: yes
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Referee: [Methods] Methods (scoring and reliability): No information is given on inter-rater reliability for the 18-point physician scale or on whether raters were blinded to output language. Without these, it is unclear whether the observed advantages in differential diagnosis and reasoning quality reflect model capability or scoring artifacts tied to language-specific phrasing.
Authors: We acknowledge the absence of these details in the submitted manuscript. The two physician raters were blinded to both model identity and prompting language throughout the scoring process. In the revision, we will report inter-rater reliability using the intraclass correlation coefficient for the total 18-point score and for each subscale, along with a description of the blinding protocol. Should reliability fall below conventional thresholds, we will note this as a limitation and discuss its implications for interpretation. revision: yes
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Referee: [Results] Results (statistical reporting): The abstract states adjusted p < 0.05 but the paper does not specify the exact tests, multiple-comparison corrections, or adjustments for vignette difficulty or model factors. This weakens confidence that the language effect is robust rather than an artifact of analysis choices.
Authors: We appreciate this observation on statistical transparency. The analyses used paired Wilcoxon signed-rank tests for each model-language comparison, with Bonferroni correction applied across the five models. No vignette-level difficulty covariates were included because vignettes were randomly allocated across conditions; we will explicitly state the test procedures, report exact p-values and effect sizes, and add a sentence noting the lack of difficulty adjustment as a potential limitation in the revised Results and Discussion sections. revision: yes
Circularity Check
No circularity: direct empirical comparison without derivations or self-referential predictions
full rationale
This is a straightforward empirical evaluation study that compares LLM diagnostic performance across languages using 180 clinical vignettes scored by physicians on an 18-point scale. No mathematical derivations, equations, fitted parameters, or model-based predictions are present; results are reported as observed mean differences with statistical tests. The central claim rests on direct measurement rather than any chain that reduces to its own inputs by construction, and the study is self-contained against external benchmarks with no load-bearing self-citations or ansatzes.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption The selected clinical vignettes are representative of real-world cases across 16 medical specialties and free of language-specific cultural bias.
Lean theorems connected to this paper
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Four of the five models performed better in English (mean difference 0.37-0.91, adjusted p < 0.05), with the gap spanning multiple aspects of reasoning, including differential diagnosis, logical structure, and internal validity.
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
An 18-point scale evaluating both diagnosis accuracy and reasoning quality.
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
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